Peak sun hours in Delaware
Delaware averages 4.2 peak sun hours a day across the year, 30th of the 50 states. At that figure a 400-watt panel produces about 1.29 kWh a day after real-world losses, and covering the 900 kWh average US bill takes about 23 panels. Wilmington, the state's biggest city, sits at 4.2 hours, close enough to the statewide figure to use either, though elevation and distance from water still move the number street by street.
modest sun: 4.2 of a possible ~6.5 hours
Panel counts for Delaware bills
Computed at Delaware's 4.2 hours with 400W panels and the 0.77 derate; the US-average column shows what the same bill takes at 4.5 hours, so you can see what your state's sun is worth in hardware.
| Monthly usage | Delaware | System size | US average |
|---|---|---|---|
| 500 kWh/mo | 13 panels | 5.2 kW | 12 panels |
| 750 kWh/mo | 20 panels | 8 kW | 18 panels |
| 900 kWh/mo | 23 panels | 9.2 kW | 22 panels |
| 1,000 kWh/mo | 26 panels | 10.4 kW | 24 panels |
| 1,500 kWh/mo | 39 panels | 15.6 kW | 36 panels |
| 2,000 kWh/mo | 51 panels | 20.4 kW | 48 panels |
What 4.2 hours means in practice
Delaware runs 7% below the national solar average, 30th of 50 at 4.2 hours. That is workable sun, not bad sun: the 900 kWh bill takes 23 panels here versus 22 nationally, 1 more. Germany built the world's densest solar fleet on worse.
How a Delaware year is shaped
The 4.2-hour figure is an annual average, and no month is average. These are the twelve monthly means for Delaware from NASA's 2001-2020 solar climatology, each as a share of the state's own annual mean, with that share applied to the 4.2-hour planning figure. June and December are marked.
| Month | Share of the annual average | Peak sun hours (est.) |
|---|---|---|
| January | 51% | 2.1 |
| February | 71% | 3.0 |
| March | 95% | 4.0 |
| April | 123% | 5.2 |
| May | 137% | 5.8 |
| June | 151% | 6.4 |
| July | 150% | 6.3 |
| August | 132% | 5.5 |
| September | 108% | 4.5 |
| October | 79% | 3.3 |
| November | 58% | 2.4 |
| December | 44% | 1.9 |
The gap between Delaware's best month and its worst is 3.4 to one: June at 151% of the annual average, December at 44%, or about 6.4 hours a day against 1.9. Four months carry 48% of the year's light. A grid-tied system rides that out on net metering without anyone noticing.
Half the Delaware calendar sits above the annual average and half below: April through September are the six months that beat it, carrying 67% of the year's light. April is already worth about 5.2 hours a day, so the productive half of the year starts earlier than most people expect.
Delaware's average home used 911 kWh a month in 2024 by EIA's count, within a few percent of the national 863, so the national panel counts on this page transfer here better than they do in most states. That average bill needs 24 panels across the year and 53 to be carried by December sun alone, a factor of 2.2.
Delaware is small enough, or flat enough, that the sun barely varies across it: the 2 grid cells sampled here span only 3%, south to north. The statewide 4.2 figure is a good description of the whole state, which is not something you can say about Texas or Oregon. Shade and roof pitch will move your output far more than address does.
What that sun is worth on a Delaware bill
| EIA, 2024 residential averages | Delaware | United States |
|---|---|---|
| Average home's monthly use | 911 kWh | 863 kWh |
| Price per kilowatt-hour | 16.57¢ | 16.48¢ |
| Average monthly bill | $150.87 | $142.26 |
| One 400W panel, a year's output | 472 kWh | 506 kWh |
| What that output displaces | $78 | $83 |
At 16.57¢ a kilowatt-hour Delaware sits 1% above the national 16.48¢, 16th of the fifty states on price. One 400-watt panel offsets roughly $78 of Delaware power a year. Mid-table on rates means the project lives or dies on the quote and the net-metering terms rather than on either the sun or the tariff.
Rank Delaware by what a panel earns rather than by sunlight and it moves up 8 places, from 30th to 22nd. Rates do that. Rhode Island gets less sun (4.1 hours to Delaware's 4.2) and pays 28.65¢ against 16.57¢, so one panel is worth about $54 less a year in Delaware than in Rhode Island.
Two warnings on those dollar figures. They are displaced electricity and nothing else: no install cost, no incentive, no financing, and no assumption about how your utility settles a surplus, which is the single biggest unknown in the sum. And a state average hides the utility you are actually on; 16.57¢ is every Delaware residential customer averaged together, and neighbouring territories can differ by more than the gap between two states in the ranking.
Getting a number for your address
For a location-exact figure, run your address through NREL's free PVWatts; it uses measured weather for your grid cell and will also model roof tilt and direction, which statewide numbers cannot. Then compare its annual kWh against a quote's promise before you sign anything.
Questions people ask
How many solar panels do I need in Delaware?
About 23 400-watt panels (9.2 kW) for the 900 kWh a month an average US home uses, at Delaware's 4.2 peak sun hours. For the average Delaware home specifically, which EIA measured at 911 kWh a month in 2024, it is 24. Your own bill is the variable that matters, and the calculator takes any figure.
Is 4.2 peak sun hours good for solar?
It is below the 4.5-hour national average but far from disqualifying. Panel counts run about 7% higher here for the same bill, and the December trough measured above deserves respect in any off-grid plan. Grid-tied systems ride through it on net metering.
How much is one solar panel worth a year in Delaware?
About $78. One 400-watt panel at Delaware's 4.2 peak sun hours makes roughly 472 kWh a year after the 0.77 derate, and Delaware residential electricity averaged 16.57¢ a kilowatt-hour in 2024 (EIA), which puts Delaware 22nd of the 50 states on this measure against 30th on sunlight alone. That figure is displaced electricity only. It says nothing about install cost, incentives, or how your utility settles a surplus.
Do peak sun hours change with the seasons in Delaware?
Yes, by a factor of 3.4 here. NASA's 2001-2020 climatology puts Delaware's June at 151% of the annual average and December at 44%, so the 4.2-hour figure on this page is the midpoint of a curve running from roughly 6.4 hours a day down to 1.9. Grid-tied homes bank the summer surplus as credit; off-grid designs have to size for the trough, and in Delaware that means 53 panels for an average local bill instead of 24.